Main sewer lines for structures, such as homes, restaurants and commercial buildings, run from a city sewer line at one end into the structure at the other end and are accessed by a capped clean out that is usually located proximate the structure. If the main sewer line becomes clogged, a snake or augur can be run into it through the clean out once the clean out cover is removed.
Sometimes main sewer lines, especially for older structures, become broken, cracked, offset or collapsed due to issues such as roots, frozen ground and settling of ground. When a main sewer line becomes damaged, it can be expensive to dig it up and replace it with new pipe, which is one reason why trenchless repair methods have become popular. One trenchless repair method is to install a pipe liner which is cured in place in the pipe. When such a repair has been made, an augur should not be used in the repaired pipe, after curing, because it can break down the cured line. One way to provide notice of a trenchless repair to a main sewer liner is to place a sticker or tag on the clean out; however, if such sticker or tag is removed, or becomes unreadable over time, the sewer line can inadvertently be damaged by future plumbing operations to clean the main sewer line.
Some residential and other buildings install backflow valves to prevent the main sewer line from backing up into its adjacent structure and some municipalities require a notice to be placed on the clean out when a backflow valve has been installed.
Certain commercial structures, especially restaurants, install grease traps between the city sewer line and the clean out, and some municipalities require a notice to be placed on the clean out when a grease trap has been installed.